852 research outputs found
1/t pressure and fermion behaviour of water in two dimensions
A variety of metal vacuum systems display the celebrated 1/t pressure, namely
power-law dependence on time t, with the exponent close to unity, the origin of
which has been a long-standing controversy. Here we propose a chemisorption
model for water adsorbates, based on the argument for fermion behaviour of
water vapour adsorbed on a stainless-steel surface, and obtain analytically the
power-law behaviour of pressure, with an exponent of unity. Further, the model
predicts that the pressure should depend on the temperature T according to
T^(3/2), which is indeed confirmed by our experiment. Our results should help
elucidate the unique characteristics of the adsorbed water.Comment: 11 pages, 4 figure
Measuring and reporting the capacity development performance of organizations in water and sanitation
Within the Water, Sanitation and Hygiene (WASH) sector, a range of organizations offer education and training activities. The aim of these activities is to improve access to water and sanitation services through better design and implementation of WASH interventions (Broughton & Hampshire, 1997; Cracknell, 2000). However, it is often not clear how effective education and training activities are at achieving these objectives. A key challenge is lack of clarity on how the results of education and training in WASH should be measured and reported. In order to address this issue, CAWST (The Centre for Affordable Water and Sanitation Technology) and the Centre for Engineering for Sustainable Development at the University of Cambridge conducted a review of measurement and reporting strategies of education and training organizations. Strengths, limitations and best practices were identified and used to develop recommendations for how CAWST, and other education and training organizations in the WASH sector, can improve the way they measure and report their results
Boson stars in massive dilatonic gravity
We study equilibrium configurations of boson stars in the framework of a
class scalar-tensor theories of gravity with massive gravitational scalar
(dilaton). In particular we investigate the influence of the mass of the
dilaton on the boson star structure. We find that the masses of the boson stars
in presence of dilaton are close to those in general relativity and they are
sensitive to the ratio of the boson mass to the dilaton mass within a typical
few percent. It turns out also that the boson star structure is mainly
sensitive to the mass term of the dilaton potential rather to the exact form of
the potential.Comment: 9 pages, latex, 9 figures, one figure dropped, new comments added,
new references added, typos correcte
Long-wavelength iteration scheme and scalar-tensor gravity
Inhomogeneous and anisotropic cosmologies are modeled withing the framework
of scalar-tensor gravity theories. The inhomogeneities are calculated to
third-order in the so-called long-wavelength iteration scheme. We write the
solutions for general scalar coupling and discuss what happens to the
third-order terms when the scalar-tensor solution approaches at first-order the
general relativistic one. We work out in some detail the case of Brans-Dicke
coupling and determine the conditions for which the anisotropy and
inhomogeneity decay as time increases. The matter is taken to be that of
perfect fluid with a barotropic equation of state.Comment: 13 pages, requires REVTeX, submitted to Phys. Rev.
Effective decrease of photoelectric emission threshold from gold plated surfaces
Many applications require charge neutralisation of isolated test bodies and
this has been successfully done using photoelectric emission from surfaces
which are electrically benign(gold) or superconducting (niobium). Gold surfaces
nominally have a high work function (\,eV)which should require deep
UV photons for photoemission. In practice it has been found that it can be
achieved with somewhat lower energy photons with indicative work functions of
(\,eV). A detailed working understanding of the process is lacking
and this work reports on a study of the photoelectric emission properties of
4.6x4.6 cm^2 gold plated surfaces, representative of those used in typical
satellite applications with a film thickness of 800 nm, and measured surface
roughnesses between 7 and 340 nm. Various UV sources with photon energies from
4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW, illuminated a ~0.3 cm^2
of the central surface region at angles of incidence from 0 to 60 degrees.
Final extrinsic quantum yields in the range 10 ppm to 44 ppm were reliably
obtained during 8 campaigns, covering a ~3 year period, but with intermediate
long-term variations lasting several weeks and, in some cases, bake-out
procedures at up to 200 C. Experimental results were obtained in a vacuum
system with a baseline pressure of ~10^{-7} mbar at room temperature. A working
model, designed to allow accurate simulation of any experimental configuration,
is proposed.Comment: 35 pages, 12 figure
Illusions of general relativity in Brans-Dicke gravity
Contrary to common belief, the standard tenet of Brans-Dicke theory reducing
to general relativity when omega tends to infinity is false if the trace of the
matter energy-momentum tensor vanishes. The issue is clarified in a new
approach using conformal transformations. The otherwise unaccountable limiting
behavior of Brans-Dicke gravity is easily understood in terms of the conformal
invariance of the theory when the sources of gravity have radiation-like
properties. The rigorous computation of the asymptotic behavior of the
Brans-Dicke scalar field is straightforward in this new approach.Comment: 16 pages, LaTeX, to appear in Physical Review
Modified Brans-Dicke theory of gravity from five-dimensional vacuum
We investigate, in the context of five-dimensional (5D) Brans-Dicke theory of
gravity, the idea that macroscopic matter configurations can be generated from
pure vacuum in five dimensions, an approach first proposed in the framework of
general relativity. We show that the 5D Brans-Dicke vacuum equations when
reduced to four dimensions lead to a modified version of Brans-Dicke theory in
four dimensions (4D). As an application of the formalism, we obtain two
five-dimensional extensions of four-dimensional O'Hanlon and Tupper vacuum
solution and show that they lead two different cosmological scenarios in 4D.Comment: 9 page
What are the mechanisms that support healthcare professionals to adopt assisted decision-making practice? A rapid realist review
Background
The United Nations Convention on the Rights of Persons with Disabilities (UNCRPD) establishes a right to legal capacity for all people, including those with support needs. People with disabilities have a legal right to be given the appropriate supports to make informed decisions in all aspects of their lives, including health. In Ireland, the Assisted Decision-Making (Capacity) Act (2015) ratifies the Convention and has established a legal framework for Assisted Decision Making (ADM). The main provisions of the Act are not yet implemented. Codes of Practice to guide health and social care professionals are currently being developed. Internationally, concerns are expressed that ADM implementation is poorly understood. Using realist synthesis, this study aims to identify Programme Theory (PT) that will inform ADM implementation in healthcare.
Methods
A Rapid Realist Review using collaborative methods was chosen to appraise relevant literature and engage knowledge users from Irish health and social care. The review was led by an expert panel of relevant stakeholders that developed the research question which asks, âwhat mechanisms enable healthcare professionals to adopt ADM into practice?â
To ensure the PT was inclusive of local contextual influences, five reference panels were conducted with healthcare professionals, family carers and people with dementia. PT was refined and tested iteratively through knowledge synthesis informed by forty-seven primary studies, reference panel discussions and expert panel refinement and consensus.
Results
The review has developed an explanatory PT on ADM implementation in healthcare practice. The review identified four implementation domains as significant. These are Personalisation of Health & ADM Service Provision, Culture & Leadership, Environmental & Social Re-structuring and Education, Training & Enablement. Each domain is presented as an explanatory PT statement using realist convention that identifies context, mechanism and outcome configurations.
Conclusions
This realist review makes a unique contribution to this field. The PT can be applied by policymakers to inform intervention development and implementation strategy. It informs the imminent policy and practice developments in Ireland and has relevance for other worldwide healthcare systems dealing with similar legislative changes in line with UNCRPD
Self-similar cosmological solutions with a non-minimally coupled scalar field
We present self-similar cosmological solutions for a barotropic fluid plus
scalar field with Brans-Dicke-type coupling to the spacetime curvature and an
arbitrary power-law potential energy. We identify all the fixed points in the
autonomous phase-plane, including a scaling solution where the fluid density
scales with the scalar field's kinetic and potential energy. This is related by
a conformal transformation to a scaling solution for a scalar field with
exponential potential minimally coupled to the spacetime curvature, but
non-minimally coupled to the barotropic fluid. Radiation is automatically
decoupled from the scalar field, but energy transfer between the field and
non-relativistic dark matter can lead to a change to an accelerated expansion
at late times in the Einstein frame. The scalar field density can mimic a
cosmological constant even for steep potentials in the strong coupling limit.Comment: 10 pages, 1 figure, revtex version to appear in Phys Rev D,
references adde
Naked Singularity Formation In f(R) Gravity
We study the gravitational collapse of a star with barotropic equation of
state in the context of theories of gravity.
Utilizing the metric formalism, we rewrite the field equations as those of
Brans-Dicke theory with vanishing coupling parameter. By choosing the
functionality of Ricci scalar as , we
show that for an appropriate initial value of the energy density, if
and satisfy certain conditions, the resulting singularity would be naked,
violating the cosmic censorship conjecture. These conditions are the ratio of
the mass function to the area radius of the collapsing ball, negativity of the
effective pressure, and the time behavior of the Kretschmann scalar. Also, as
long as parameter obeys certain conditions, the satisfaction of the
weak energy condition is guaranteed by the collapsing configuration.Comment: 15 pages, 4 figures, to appear in GR
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